1. Field of the Invention
The present invention relates to a method of checking pattern measurements that measures a size check pattern to check the precision of production after identifying the position of the size check pattern on a substrate by using a size check apparatus, and further relates to an image recognition assisting pattern that is used to identify the position of the size check pattern.
The method of checking pattern measurements is employed in checking measurements of a pattern formed by a lithography process or an etching process in the manufacture of semiconductor devices or the manufacture of optical devices, for example.
2. Description of the Related Art
In the manufacture of semiconductor devices, checking of measurements for patterning processes has been increasing in its significance because of needs for finer patterns. Cost consideration is important in measuring size, giving rise to complete automation as a major trend in the field.
As an example of related-art methods, a method that is widely used for checking measurements will be described in the following.
A wafer on which semiconductor devices are formed, for example, is subjected to measurement checks. The following description is provided by using a wafer by way of example. A wafer is first set in a size check apparatus. Two points on the wafer are identified for the purpose of positioning, thereby obtaining positional information regarding X, Y, and xcex8. Then, the apparatus is aligned to a size check pattern based on the obtained information. Since positional accuracy of the size check apparatus is not sufficient at this point, further positional information is obtained. Based on this accurate positional information, the size check pattern is identified, and measurements thereof are taken.
When obtaining positional information, it is necessary to perform pattern matching for image recognition and to identify the pattern as one of the registered patterns.
In summary, this method includes the following steps.
1) detecting two points on the wafer;
2) roughly measure the position of the size check pattern;
3) accurately measure the position of the size check pattern;
In general, at the step 1), image recognition is performed by use of an optical microscope. At the steps 2) and 3), an SEM (scanning electron microscope) is mostly used for the purpose of image recognition.
FIGS. 1A and 1B are illustrative drawings showing an example of a related-art size check pattern. FIG. 1A shows a plan view of the pattern, and FIG. 1B shows an area of image recognition superimposed on the plan view. A size check pattern 2 is of a type generally used. A doted-line box 4 indicates the image recognition area for the size check pattern 2, defining an area within which an image recognition process is performed. In general, the image recognition at the step 2) is carried out by using a SEM image having an enlargement factor of 3000 to 8000.
A size check is carried out by measuring a width a as illustrated by arrows in FIG. 3A.
The size check pattern 2 may be a pattern formed by etching a wafer or a substrate of other types for forming semiconductor device, or may be a resist pattern formed by photolithography.
In order to carry out image recognition of a size check pattern at the step 2), pattern matching is conducted between the size check pattern on the wafer to be checked and the registered size check patterns. If the pattern matching produces a check result exceeding a predetermined threshold, the image recognition process is completed, and the procedure goes on to the next step.
Unfortunately, however, the pattern to be measured and the registered patterns each have varying appearance depending on the conditions of manufacturing process that varies from time to time. That is, these patterns vary from one extreme to the other depending on the size and shape of formed patterns and the type and thickness of layers formed underneath. Typically, the size check apparatus is provided with various algorithms for optimizing conditions. Such algorithms, however, are not sufficiently effective, resulting in recognition errors in many cases. If the threshold is lowered to avoid a failure to recognize, erroneous recognition of a size check pattern will ensue, resulting in an increase in the labor for correcting the errors.
Accordingly, there is a need for a method of image recognition that reduces errors of image recognition during size checks, thereby improving work efficiency.
It is a general object of the present invention to provide a method of detecting a position of a size check pattern that substantially obviates one or more of the problems caused by the limitations and disadvantages of the related art.
Features and advantages of the present invention will be set forth in the description which follows, and in part will become apparent from the description and the accompanying drawings, or may be learned by practice of the invention according to the teachings provided in the description. Objects as well as other features and advantages of the present invention will be realized and attained by a method of detecting a position of a size check pattern particularly pointed out in the specification in such full, clear, concise, and exact terms as to enable a person having ordinary skill in the art to practice the invention.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method of detecting a position of a size check pattern on a substrate by using a size check apparatus so as to measure a size of the size check pattern for a purpose of checking precision of production, the method comprising the steps of a) providing image recognition assisting patterns on the substrate on both sides of a portion to be measured of the size check pattern, b) setting the size check apparatus to have an image recognition area that includes both the size check pattern and the image recognition assisting patterns; and c) detecting the position of the size check pattern by use of the size check apparatus based on the size check pattern and the image recognition assisting patterns.
In the method described above, the image recognition assisting patterns are provided on both sides of the portion to be measured of the size check pattern, so that it is possible to bring the black and white contrast of the image recognition area closer to an optimal setting than in the case of no image recognition assisting patterns. This lowers the rate of image recognition errors, and improves a work efficiency of pattern size checks.